碱熔-二次沉淀分离-电感耦合等离子体质谱法测定贵州古陆相沉积型稀土矿中16种稀土元素及铌、钽、锆、铪的含量

Determination of 16 Rare Earth Elements,Niobium,Tantalum,Zirconium,and Hafnium in Paleocontinental Sedimentary Rare Earth Ores in Guizhou by Inductively Coupled Plasma Mass Spectrometry with Alkali Fusion and Secondary Precipitation Separation

贵州古陆相沉积型稀土矿样品主要含锐钛矿、高岭石、赤铁矿等副矿物,难以被微波消解法完全分解。通过优化样品分解、浸取方法,提出了题示方法。取0.1 g样品于刚玉坩埚中,加入约2.5 g过氧化钠,混匀后再铺上约0.5 g过氧化钠,于750℃熔融15 min。置于盛有50 mL含5 g·L^(-1)硫酸镁和5 g·L^(-1)氯化铵的热溶液中浸取10 min,加热煮沸1~2 min。加入5 mL 50%(体积分数,下同)氨水溶液,搅匀后静置60 min。用滤纸过滤,沉淀用40 mL热的50%(体积分数,下同)硝酸溶液分次溶解,将所得溶液加热煮沸1~2 min,用50%氨水溶液调节溶液酸度至p H 8~10,用滤纸过滤,沉淀用40 mL热的50%硝酸溶液分次溶解,用2 g·L^(-1)酒石酸溶液稀释至200 mL,在动能歧视(KED)模式下用电感耦合等离子体质谱仪分析。结果显示:采用含硫酸镁和氯化铵的热溶液加热浸取有助于碱性溶液中铌、钽形成铌酸镁和钽酸镁沉淀析出;氨水-铵盐体系中可将铌、钽、锆、铪以及稀土元素定量沉淀;用氨水调节酸度进行二次沉淀分离提纯,能除去大部分基体元素与试剂引入的盐类;采用KED模式以及在线内标校正能降低质谱干扰,尤其对于钪元素。在优化的试验条件下,20种分析元素的质量浓度均在1.00~1000μg·L^(-1)内和内标103Rh校正后的质谱强度呈线性关系,检出限为0.010~1.66μg·g^(-1);用一级国家标准物质进行验证,所得各分析元素测定值的相对误差为0.030%~16%,相对标准偏差(n=7)为2.1%~14%。

Paleocontinental sedimentary rare earth ore samples in Guizhou mainly contains accessory minerals such as anatase,kaolinite,and hematite,which were difficult to completely dissolve using conventional microwave digestion process.By optimizing the sample decomposition and extraction methods,a method mentioned by the title has been proposed.An aliquot(0.1 g)of the sample was placed into a corundum crucible,and about 2.5 g of sodium peroxide was added.After mixing thoroughly,about 0.5 g of sodium peroxide was added on top.The mixture was melted at 750℃for 15 min,and the frit was immersed in 50 mL of the hot solution containing 5 g·L^(−1) magnesium sulfate and 5 g·L^(−1) ammonium chloride for 10 min.After boiling for 1-2 min by heating,5 mL of 50%(volume fraction,the same below)aqueous ammonia solution was added.After stirring thoroughly,the mixture was settled for 60 min,and filtered by the filter paper.The precipitate was dissolved in 40 mL of hot 50%(volume fraction,the same below)nitric acid solution in portions,and the resulting solution was boiled for 1-2 min by heating,whose acidity was adjusted to pH 8-10 with 50%aqueous ammonia solution.After filtering with the filter paper,the precipitate was dissolved in 40 mL of hot 50%nitric acid solution in portions,diluted to 200 mL by 2 g·L^(−1) tartaric acid solution,and analyzed using inductively coupled plasma mass spectrometer in KED mode.It was shown that heating leaching with the hot solution containing magnesium sulfate and ammonium chloride helped to form magnesium niobate and magnesium tantalate precipitates from niobium and tantalum in alkaline solution.In the aqueous ammonia-ammonium salt system,niobium,tantalum,zirconium,hafnium,and rare earth elements could be quantitatively precipitated.Using ammonia water for secondary precipitation separation and purification could remove most of the matrix elements and salts introduced by reagents.The use of KED mode and online internal standard correction could reduce mass spectrometry interference,especially for scandium element.Under optimized experimental conditions,linear relationships between values of the mass concentration of the 20 analytical elements and mass spectrometry intensity calibrated by internal standard of 103Rh were kept in the range of 1.00-1000μg·L^(−1),with detection limits in the range of 0.010-1.66μg·g−1.Verified test was made on first-class national reference materials,and the relative errors of the determined values of analytical elements were found in the range of 0.030%-16%,giving RSDs(n=7)in the range of 2.1%-14%.